Unit 6 - Breathing Circuits Flashcards
examples of open circuits
- insufflation
- simple face mask
- nasal cannula
- open drop
examples of semi-open circuits
- Mapleson
- circle system (FGF > Vm)
examples of semi-closed circuits
circle system (FGF < Vm)
example of closed circuit
circle system with very low FGF, APL closed
Benefits of low FGF in circle system
- Increased humidity
- Slower ↓ in temp
primarily influences rebreathing
- FGF
- Arrangement of components in circle system
- Functioning unidirectional valves
3 different configurations possible with circle system and what determines which one it is
- semi-open
- semi-closed
- closed
depends on FGF and APL
purpose of unidirectional valves
ensure that gas only travels in one direction
example of how a circle system can be semi-open
using 10 L/min flow during induction
example of how a circle system can be a semi-closed system
reducing FGF to 2 L/min after intubation
example of how a circle system can be closed
FGF just enough to support gas consumption
Advantages of circle system
- Consistent inspired gas concentrations
- Maintains heat and humidity
- Low resistance (not as low as Mapleson)
- Can be semi-open, semi-closed, or closed
- Minimizes OR pollution
disadvantages of circle system
- Multiple places for disconnect to occur
- Less portable than non-rebreathing
- Unidirectional valves can malfunction
adverse effects of malfunctioning unidirectional valves
- Stuck open: rebreathing
- Stuck closed: airway obstruction
purpose of reservoir bag in circle system
- protects patient against excessive airway pressure during SV
- Allows you to generate positive pressure to deliver assisted or controlled ventilation
- permits rebreathing and use of lower FGF
most distensible component of breathing system
Reservoir Bag
ASTM (American Society for Testing and Materials) requires that pressure inside adult-sized reservoir bag does not exceed internal pressure of ____ cm H2O if bag inflated up to ____ its size
60
4x
determines how much pressure can be generated inside circuit in bag mode
APL valve
acts like a stopcock that diverts gas flow to APL and bag or ventilator
Bag-Vent Selector Switch
where does dead space begin & end when unidirectional valves work properly
begins at Y piece
ends in terminal bronchioles
position of unidirectional valves during breathing cycle
- Inspiratory valve is open during inspiration and closed during expiration
- Expiratory valve is closed during inspiration and open during expiration
2 causes of increased inspired CO2
- Incompetent unidirectional valve
- CO2 absorbent exhaustion
what should be done in the event of an incompetent valve that can’t be fixed
a closed or semi-closed system should be converted to semi-open
2 options if absorbent is exhausted during procedure
1) convert closed or semi-closed to semi-open by increasing FGF to 5-8 L/min
2) Change absorbent
how does increasing Vm affect increased inspired CO2 d/t absorbent exhaustion
will NOT prevent CO2 rebreathing - must increase FGF
which Mapelson is best and worst for spontaneous ventilation
best = Mapelson A
worst = B
fresh gas inlet & APL location in Mapelson A
- fresh gas inlet = near bag
- APL = near patient
fresh gas inlet & APL location in Mapelson B
inlet = near patient
APL = near patient
fresh gas inlet & APL location in Mapelson C
inlet = near patient
APL = near patient
fresh gas inlet & APL location in Mapelson D
inlet = near patient
APL = away from patient
fresh gas inlet & APL location in Mapelson E
inlet = near patient
APL = away from patient
fresh gas inlet & APL location in Mapelson F
inlet = near patient
APL = not present
which Mapelson circuit does not have a reservoir bag
E
which mapelson circuit does not have corrugated tubing
C
which mapelson doesn’t have APL or reservoir bag
E
how is rebreathing minimized with a mapelson
higher FGF, smaller Vt, and longer expiratory time
best method of determining FGF required to prevent rebreathing with Mapelson
EtCO2
advantages of mapelson circuits
- Less airway resistance (good for peds)
- Convenient
- Easily scavenged
- Bain circuit prevents heat loss
disadvantages of mapelson circuits
- Increased apparatus dead space
- Requires high FGF to prevent rebreathing
- Loss of heat and humidity
- Inefficient use of inhaled anesthetics
- Risk of environmental pollution
- Unrecognized kinking of fresh gas hose in Bain circuit
best and worst mapelson for controlled ventilation
- Best: Mapleson D (DFE > BC > A)
- Worst: Mapleson A
general rule for FGF in mapelson circuit
what’s the exception
FGF ~2.5 times patients Vm to prevent rebreathing
Exception: Mapleson A requires FGF ~20 L/min during CV
other factors besides FGF that affect rebreathing in Mapelson
- Vm
- mode of ventilation
- RR
- Vt
- inspiratory flor rate
- I:E
- volume of reservoir bag
- volume of corrugated tubing
- use of mask/LMA/ETT
what is the Bain system
- Modified Mapleson D
- FGF enters circuit through thin inner tubing, exhaled gas exits via corrugated tubing
how is rebreathing prevented with Bain circuit
FGF should be 2.5x minute ventilation
what test is performed as part of preanesthetic check out in Bain system
- Occlude elbow at patient end
- Close APL
- Use O2 flush to fill circuit
- Remove occlusion at elbow while flushing circuit
results of Pethick test that mean Bain system is safe to use
Venturi effect will cause reservoir bag to collapse (circuit is safe to use)
results of Pethick test that mean Bain system is not safe to use
If inner tubing is occluded, reservoir bag will remain inflated
what type of breathing circuit does not contain dead space
open
all other circuits are closed to atmosphere and contain some degree of d
what type of breathing circuit does not contain dead space
open
all other circuits are closed to atmosphere and contain some degree of d
which 3 mapelson circuits are most likely to be encountered in modern anesthesia practice
D, E, F
what type of breathing circuit are Mapelsons
all are semi-open or non-rebreathing
what type of circuit contains a reservoir bag but does not allow rebreathing of exhaled gases
semiopen
what type of circuit contains a reservoir bag but does not allow rebreathing of exhaled gases
semi-open
what’s different about a Bain circuit vs. Mapelson D
fresh gas travels towards the patient through a smaller tube inside the corrugated tubing
how is incoming fresh gas warmed by Bain system
by the exhaled gas
